Simultaneous occurrence of a thyromediastinal muscle, a truncus bicaroticobrachialis, and a left superior vena cava

A case is presented of a combination of anatomical anomalies found in a 67-year-old female cadaver during routine dissection by medical students. They include a thyromediastinal muscle, a truncus bicaroticobrachialis, and a left superior vena cava, with complete absence of the right superior vena cava, but with a normal azygos vein opening into the right atrium at the expected site of entry of the superior vena cava. No associated congenital cardiac malformations were found. Clinical implications include the difficulty of heart catheterization through the subclavian veins and misleading images on CT or MRI scans, where the azygos vein could be mistaken for a right superior vena cava.